Means for producing a variable number of pulses



Jan.2, 1951 c. E. CLEETON MEANS FOR PRODUCING A VARIABLE NUMBER OFPULSE-S Filed Dec. 12, 1939 2 Sheets-Shet 1 IN v5 ran Cldud E. Clea tonATTURNE Y Jan. 2, 1951 C- E. CLEETON MEANS FOR PRODUCING A VARIABLENUMBER OF PULSES Filed Dec. 12, 1959 2 Sheets-Sheet 2 i 97 9 85? I I I II I I I l I I I I I l I l i I l I I I i l I I l I I I l i 94 93' 92 9 90I l F I I I I I I l l I I I I 1 I I l I i I I I l i I l I I l I i I I II I I l I l i L 1 I 1 1 l 1 l L I 1 E; E

99 l0 /0/ lfiZ I l I I I my I l I I I i l t /fll 7 =1 INVENTOR ATTOHWEYPatented Jan. 2, 1951 UNITED STATES ATENT OFFICE MEANS FUR PRUD UCING AVARIABLE NUMBER OF PULSLES (Granted. under the act of March 3,. 1883, as

amended April 30,. 1928.; 370 0. G. 757.)

This invention relates to apparatus forproducing groupsof pulsesofalternating curent or voltage whereby'the number of pulses in a groupmay be selectively predetermined.

Amongthe several" objectsof this invention are:

To provide meansfor-producing current or voltage pulses in groups ofvarying number:

To provide means of'thetype-specified having a plurality-of stages. thatare combinable in diner q ent arrangements to give a number of pulsegroupings much greater than the number of stages employed;

To provide apparatus: of the type specified wherein the number of"stages may be; varied to produce" any desired numberof pulses per groupup to the .maximum of which the system is capable;

To provide simple means for predetermining the number'of pulses pergroup.

The manner in which the foregoing and other objects are attained willmorefully' appear when the following specification is read in connectionwith the drawings wherein:

Fig. 1 is a: schematic drawing of one embodiment of the presentinvention;

Fig. 2' is-a diagram" of amultivibrator circuit wherein oscillation maybe started and stopped by varying the potential on the-grid of one ofthe tubes;

Fig. 3 depicts-schematically a multivibrator controlled by a tube thatis in turn governed by varying current in a resistor;

Fig. 4 shows schematically how a keyboard may bearranged to select thenumber of pulses in a group;

Fig. 5 is a diagramof a switching arrangement fcrsel'ecting thenumber ofpulses in a group when it is not necessary that the change fromone'numher to anotherbe quickly effected.

The'present invention comprehends, in general, amultivibrator oscillatorcontrolled by an electronic scale-of-two? counter and an electronicswitch to control" the oscillator. Any type of conntermay beutilizedinthis system if it meets the requirements of. speed andreliability.

Referring now to Fig. 1, the: tubes 5 and have their anodesMB. and 9.connected to a common anode supply It through. resistors I! and I2,respectively, and their screen grids l3. and I4 connected to the samesource H! through the resistors l5-and l5, respectively. Capacitors I1and I8, respectively, couple the anodes B and 9 to the grids 2B and H!of the tubes and 6 whereby the drop-of potential. across the resistors Hand I2 when. the; respective: tubes draw current is: 811

plied to the second grid of the othertube-tohold such. other tubeinnon-conducting condition; Grids Iii-and Zil-are connected tothe catliodes zl and 22 of the respective tubes through resistors 2-3 and 24;

The electronic counter is inthe' instance-depict ed in Fig. 1, madeup:of fourstages designated generally as 25-, 25; 2? and 28. All of thesestages identical and the description of one applies equally to theothers: Itwill be observed that stage 25 includesa first tube 29 and asecond tube having anodes 2H and-32 connected to acommon supply E 5through resistors: 33 and 3d, the second grids 35 and te being connectedtoxa common supply Eg through resistors 31 and 38 respectively. Theanodes-31 andte are respectively connected through resistors 39 audtsand shunting capacitors-39 and ie to the second grid (35 or 35) of theother tube. Screen grids ti andWZ areconnected to a common-supplyES.First'grids and i t have a common connection througli t5- and 46-tocapacitor'fl whereby the first grids-fitand't i arecoupled' teanode 8of tubeB; thesaid first-gridsbeing also connected to -grou'nd' throughresistor" 48-3 It will be apparent; from the foregoing that when themultivibrator tubes 5 and. l. are oscils latingr; a. negative.- P111581will: be transmitted; through capacitor 41 to the first grids 43.sandl44 of the tube-size; an'dl30;.sa1ppingv the flow OfiflllK- rentthrough the tube; that: may. be: conducting. at;

that particular: time and. causing the: other tube: in;thestagetcconduct; If. it be assumed, for purpose of illustration, that;tube; 2.91: is conducting: when. the negative. pulse: is. applied, the.flow oft currentthrough tube-.29. will. be. arrestedand; the;-

resultantrise. of: potential on anode. 3i will-heap pliedthroughresistonfiii and; capacitor 319." to-gridw 3% ot tnbewiiiithereby causing the tube; (iii to. be,-

come conductingawwhich inuturn. will apply. the: potential: drop. acrossresistor. to grid 3510i tube: 2.9. to. hold tube; 2 9. .in 1 the 1non-econducting condition.. At the-same timehtheqpotential drop. across:resistor 3.4;: will. be transmitted through. capacitor:

tube 35 to tube 29 Will not apply a negative pulse to grids 58 and andhence the conductive condition of tubes 52 and 53 will remain unchanged.

First grids 54 and 55 of tubes 56 and 57 in stage 21 are likewisecoupled to the anode 58 of tube 53 by capacitor 59 and capacitor 60couples anode 6| of tube 5l' to first grids 62 and 63 of tubes 64 and 65in stage 28.

Tubes 66 and 61 in switching stage 68 have their anodes 69 and 10, theirsecond grids H and 12 and their screen grids i3 and 74 connected in thesame manner as do the tubes in stage 25 above described. However, onlyfirst grid 15 of tube 66 is coupled to the anode of tube 65 throughcapacitor 16, the first grid ll of tube 61 being coupled throughcapacitor 78 to a keying or external control source. Anode 16 of tube 61is connected by lead 19, through parallel connected resistor 80' andcapacitor 8| to the first grids 82 and 83 of multivibrator tubes 6 and1.

It is obvious that when tube 61 is conductive, the potential dropthrough resistor 84 is applied to first grids 82 and 83 of themultivibrator tubes 6 and I and oscillation of the multivibrator isprevented. However, if a negative pulse be applied through capacitor 18to first grid ll of tube 61, the flow of current through tube 61 will bearrested and the tube 66 will become conductive, the consequent rise ofpotential on anode being transferred to grids 82 and 83 and themultivibrator being set into operation.

-As is well known, the multivibrator operates by automatically changingthe condition of conductivity of the tubes in the multivibrator circuitand hence the tube 6 will be made alternately conducting andnon-conducting, with the concomitant application of a negative pulse tofirst grids 43 and 44 of tubes 29 and 30 each time the tube 6 becomesconducting.

A simple expedient for determining which tube in each of the stages 25to 28 shall be conducting is to open the ground connection of one of thetubes and thus necessarily the other tube in the stage will conduct. Thenumber of pulses in any one group is determined by the condition of thecounter stages before the group starts, since this will control thenumber of changes in conductivity'of stage 25 necessary to go throughthe required series of combinations of operating conditions in theseveral stages to block tube 66 in switching stage 68 and thereby causetube 61 to become conductive and stop the multivibrator.

As an example of the foregoing, let it be assumed that cathodes 85, 86,81 and 88 of tubes 36, 53, 56 and 55, respectively, be open circuited,thereby causing tubes 29, 52, 51 and 64 to be in aconductive condition.As soon as the flow of current in these tubes is established the cathodecircuits that were opened may be closed and the apparatus is conditionedfor operation. A negative pulse is now applied to first grid Tl of tube61 with the resultant beginning of oscillation of the multivibratortubes 6 and I. When tube 6 passes current, a negative pulse is appliedto grids 4 3 and 44 of tubes 29 and 38 and, since tube 29 has beenassumed to be conducting, this tube will be blocked and tube 30 will berendered conductive which will in turn result in the application of anegative pulse through capacitor 49 to grid 50 of tube 52 and will blocktube 52 while making tube 53 conductive. The negative pulse throughcapacitor 59 to grids 54 and 55 of tubes 56 and 51 will change theconductivity in' stage 21 from tube5l to tube 56 but since tube 51 isnow rendered non-conducting there will be no change in assaoas 4 stage28 and the conditions of conductivity in the various stages thus set upwill continue until tube 6 again conducts and another negative pulse isapplied through capacitor 41 to grids 43 and 44 of tubes 29 and 30.

If the notation 29 to 36 be used to designate that tube 29 is blockedand tube 30 becomes conductive, the sequence of operation will be asfollows for the set-up that was assumed to have been established:

First pulse-26 to 30, 52 to 53, 5"! to 56; Second pulse-30 to 29;

Third pulse29 to 36, 53 to 52;

Fourth pulse-48 to 29;

Fifth pulse29 to 3B, 52 to 53, 56 to 57, 64 to 65.

It is obvious that when tube 65 becomes conductive, a negative pulsewill be applied through capacitor is to grid '15, that tube 61 will thusbe rendered conductive and the oscillation of the multivibrator will bestopped and a group of five pulses will have been applied through outputcapacitor 89 to Whatever instrumentality is controlled by the pulses.For example, a transmitter may be keyed to transmit a pulse each time apulse is passed by capacitor 85, i. e.,- each time tube 6 becomesconducting. It will be apparent from the foregoing that any number ofpulses in a group, from 1 to 16, may be transmitted by suitable settingof the conductivity conditions in the tubes of the stages 25 to 28. If agreater number of pulses per group should be desired it is necessarymerely to add additional counter stages to the circuit and by suitablepermutations to secure the desired number of pulses per group.

If it be desirable to change rapidly the number of pulses per group, akeyboard may be arranged whereby the cathode circuits of the tubes I instages 25 to 28 may be opened in any desired combinations. Fig. 4 showsa key arranged to open simultaneously contacts SI, 62, 93 and 94 tobreak the connections to ground of cathodes 85, 86, Si and 88 abovedescribed while leaving the cathodes 95, 56, 91 and 98 connected toground to permit the respective tubes 28, 52, 57 and64 to conduct. It isapparent that a keyboard of sixteen keys similar to 96 may bearranged tocontrol the sixteen combinations of cathode connection and permitinstantaneously changing the number of pulses per group.

Fig. 5 shows a double-pole, double-throw switching arrangement wherebythe'conductivity conditions of the tubes in the several stages may becontrolled when rapid shift of the number of pulses per group is notrequired. With the connections of switches 66, I66, EDI and H12 asshown, when solenoid i633 is energized, contact 64 is opened and theset-up previously described is established. By suitably changing thesettings of switches 9a to 162, the whole range of combinations may beattained and the number of pulses may be varied over the possible rangeestablished by the number of counter stages.

In Fig. 2 is depicted a multivibrator circuit employing triodes in themultivibrator instead of pentagrid tubes as in Fig; 1.

The anode supply M15 is connected through resistors 96 and E6? to anodesI68 and 269 of tubes HQ and Hi, the anodes I68 and 65 being respectivelycoupled by capacitors i IZ'and H3 to. grids H5 and N of the other tubeand the grid its being connected by lead 7! to switching stage 63. V H

Fig. 3 illustrates a different method of control, using the triodemultivibrator of Fig. 2. Anode (it: of tube Hi is connected to,anodesupply- Hi through anode resistor [ill or tube Hi, and grid MB oftube i ill is connectedtoisupply 510,5 through grid current limitingresistor ltd. Plate supply Ep is connected to grid I29 of tube ill;through a resistor iii and the tubes 29, 52, 55, and; derive their platecurrent from lead I22; tl ugh resistor l2: instead of directly fromsupply Consequently, when any one oi the tubes; 2:9, 5 2;, 56 S isdrawing curr n tube Mlhlcv Howevenwhennone of tubes 28,, 52 St or 655,conducting, tube M Ti becomes conduetive and the drop across resistorlil'l so reduces the poten a. on anode Hi9 that tube H t willnqtdraw cuand the multivibrator cannot o H condition of the counter stages 25 tthat; oscillation of the n ultivibrator is th nor-rent the tubes as, 52,56 or 64, draws, cur ent and cones, quently with the apparatus Qf Fig.3, and the corn ductivity conditions as above describ d, he Hum ber ofpulses per group with the device of Big, 3 will be determined exactlyasin Fig. l

The wave form of the pulse is deter: inedenly by the constants of theelectronic os later u d. The frequency of the pulses be anything fromone cycle every few seconds to several thousand per second and isdetermined only by the limit of frequency of oscillation of the1nultivibrator oscillator and the electronic counters associated withthe system, Equipment embodying this invention has been operated at33,009 cycles with a maxinnuncf 512 pulses per group. If it is desiredto space the pulses closer to gether, the maximum number transmitted pergroup has to be decreased or the time constants of the counting circuitsdecreased,

The invention described herein may be manufactured and/or used by or forthe Govern 3'6 of the United States of America torgovernmen purposeswithout the payment of any royalties thereon or therefor.

I claim:

1. Apparatus for producing a variable nu of voltage pulses in a group,comprising a mu 1 vibrator oscillator including two vacuum tubes eachhaving a cathode, an anode, firstandsecond grids and a screen grid,anode supply means, a es e r st nce on e n each said anode and screen anto idsurn y; me n a sed: tance connecting each, saidanode to, the secondgrid of the other tubes; variable counter means comprising a pluralityof stages, a, switching stage, each said stage including a first and asecond vacuum tube each havinga cathode, an anode, first and. secondgrids and ascreen grid; grid, screen grid and anode supply means com,-mon to all tubes of all said stages, ares resistance connecting eachsaid anodeto s id common anode supply, a respective resistanceconnecting the secondgrid of each tube in allsaid stages to said commongrid supply, a resistance and capacitance in parallel connecting theanode of each tube in each said stage; to the; second grid of the othertube in the same; stage, a capacitance coupling the anode of the secondtube in each counter stage to thefirstgrids, of both tubes in the nextsucceeding stage 'W'hfil'fi? by the potential drop across the anoderesistor of a second tube when such tube passes current is impressedupon the first grids of the tubes in the said succeeding stage toreversethe conductivity conditions of such tubes, a grid leak resistanceconnected to thefirst grids in the tubes of each stage, a capacitancecouplingtheanode of thelsecond tube in thelast counten stage totheillstglldofthe firsttube in theswitching sta e. a capacitance couplingthe anode of one of said inultivibrator tubes to the first grids of thetubes in the first counter stage, means, connecting the anode connectedterminal of the anode resistance of the second tube in said switchingstage to the first grids of the multivibrator tubes, meansto impress anegative potential on the first grid of the second tube, in saidswitching stage, and output means coupled to the anode of said one ofthe multivibratortubes.

2; Apparatus for producing a variable number of voltage pulses in agroup, comprising a multivibrator oscillator including two vacuum tubes.a plurality of counter stages each including a first, and a secondvacuum tube each of' which has an anode, a cathode and first and secondgrids, anode supply means, a respective anode resistance connecting eachanodeto saidsupply, means to apply to the second grid of each tube thepotential drop across the anode resistance of the other tube in the samestage, whereby when one tube in a stage is passing current the othertube in the same stage is held non-com ducting until changed byapplication of an externally derived voltage, means to apply to thefirst grids of both tubes in a stage changes of potential at the anodeof the second tube in the preceding stage whereby to change theconductivity conditions of the tubes in each stage to which a negativepotential is thus applied, means to apply to thefirst grids of the tubesin the first stage a negative potential from one tube in saidmultivibrator to reversethe conducting conditions of the tubes in saidfirst stage, a switching stage including a first and a second vacuumtube each having a cathode, an anode, first and second grids, arespective anode resistor connecting the anode of each tube in saidswitching stage to said anode supply, means to impress upon the firstgrid of'the first tube in said switching stage a potential drop acrossthe anode resistor of the second tube in the last counter stage, meansto impress upon the first grid of the second tube in said switchingstage an externally derived negative potential, means to impress uponthe first grids of the said multivibrator tubes the drop in potentialacross the anode resistor of said second tube in the switching stage,and output means coupled to the anode of said one tube of saidmultivibrator.

3. Apparatus for producing a variable number of voltage pulses in agroup, comprising a multivibrator oscillator including two vacuum tubes,a plurality of counter stages each including a first and a second vacuumtube each of which has an anode, a cathode and first and second grids,anode supply means, a respective anode resistance connecting each anodeto said supply, means to apply to the second grid of each tube thepotential drop across the anode resistance of the other tube in the samestage, whereby when one tube in a stage is passing current the othertube in the same stage is held nonconducting until changed byapplication of an externally derived voltage, means to apply to thefirst grids of both tubes in a stage changes of potential at the anodeof the second tube in the preceding stage whereby to change theconductivity conditions of the tubes in each stage to which a negativepotential is thus applied, means to apply to the first grids of thetubes in the first stage a negative potential from one tube in saidmultivibrator to reverse the conducting conditions of thetubes in saidfirststage, and switching means controlled by a negative potential dropacross the anode resistor of the second tube in the last counter stageto stop said multivibrator from operating.

4. Apparatus for producing a variable number of voltage pulses in agroup, a self-oscillatory device for generating periodic voltage pulses;variable counter means comprising a plurality of stages, a switchingstage, each said stage including a first and a second vacuum tube eachhaving a cathode, an anode, first and second grids and a screen grid;grid, screen grid and anode supply means common to all tubes of all saidstages, a respective resistance connecting each said anode to saidcommon anode supply, a respective resistance connecting the second gridof each tube in all said stages to said common grid supply, a resistanceand capacitance in parallel connecting the anode of each tube in eachsaid stage to the second grid of the other tube in the same stage, acapacitance coupling the anode of the second tube in each counter stageto the first grids of both tubes in the next succeeding stage wherebythe potential drop across the anode resistor of a second tube when suchtube passes current is impresesd upon the first grids of the tubes inthe said succeeding stage to reverse the conductivity conditions of suchtubes, a grid leak resistance connected to the first grids in the tubesof each stage, a capacitance coupling the anode of the second tube inthe last counter stage to the first grid of the first tube in theswitching stage, a capacitance coupling said device to the first gridsof the tubes in the iirst counter stage whereby a negative pulse fromsaid device changes the conductivity condition of the tubes in saidfirst stage, means connecting the anode connected terminal of the anoderesistance of the second. tube in said switching stage to apply anegative potential to said device to inhibit operation of said devicewhen said second switching tube is conducting for the first grids of themultivibrator tubes, means to impress a negative potential on the firstgrid of the second tube in said switching stage, and output meanscoupled to said device to transfer pulses for utilization externally ofsaid apparatus.

5-. Oscillatory apparatus, comprising two vacuum tubes each having acathode, an anode, and a grid, anode supply means, a respective re orconnecting each said anode to said supply a respective capacitorcoupling eac '1 to the grid of the other tube; a third vacuum tubehaving a cathode, an anode, a screen grid, a suppressor grid and acontrol grid, means connecting the anode of said third tube to the anodeof one of said two tubes, means connecting said screen grid to saidanode sup-ply, a second anode supply circuit including a resistor havinga high potential end connected to the cathode of said third tube and alow potential end connected to the control grid of said third tubewhereby current flow in said second anode supply circuit plies anegative potential to said control grid, means connecting said highpotential end to said suppressor grid and to the cathodes of both saidtwo tubes, and a respective grid resistor connecting each grid of saidtwo tubes to the cathodes thereof.

6. Apparatus as described, comprising a multivibrator oscillator,counter means includi plurality of stages each having two e conductingpaths, a first one of said stages being connected to have the currentchanged from one path to the other by a negative pulse from saidmultivibrator, electronic switching means having two alternativeconducting paths, a last stage of said counter means having One saidpath connected to apply a pulse to one path in said switching means, allsaid stages except said last stage having each one path connected toapply a negative potential to change the flow of current from one pathto the other in the next succeeding stage, and means connecting theother path in said switching means to apply a pulse to stop saidmultivibrator when a pulse is applied to said one path of said switchingmeans as aforesaid.

7. Apparatus as described, comprising a multivibrator oscillatorincluding two vacuum tubes each having an anode, a third vacuum tubehaving an anode and a control grid, a first resistor connected in serieswith the anodes of said third tube and one of said multivibrator tubes,an anode supply circuit including a resistor in series with said controlgrid whereby when current flows in said anode supply circuit said thirdtube is blocked, but when no current flows in said anode supply circuitsaid third tube draws current and said multivibrator is blocked.

8. An apparatus for producing a group of periodic pulses in precise timerelation with a controlling influence comprising periodic pulsegenerating means, means initiating operation of said generating means inprecise synchronism with said controlling influence, counting means forthe generated pulses, means terminating operation of said generatingmeans when a predetermined number of pulses are counted by said countingmeans, and selectively operable means for varying said predeterminednumber.

9. An apparatus for producing a predetermined number of pulses in agroup comprising periodic pulse generating means, a control signal,means responsive to said control signal initiating operation of saidgenerating means to produce periodic pulses in synchronism therewith,counting means for the produced pulses, and means terminating operationof said generating means when a number of pulses equal to saidpredetermined number are counted by said counting means.

10. An apparatus for producing a variable number of pulses in a group,comprising an oscillator for generating voltage pulses, electroniccontrol means connected to the oscillator to initiate and terminateoperation thereof, said electronic control means including meansoperative responsively to a control signal to initiate operation of theoscillator in exact phase relation therewith, permuting counter meanshaving a plurality of stages including one stage coupled to theoscillator, means conditioning said stages to interact in apredetermined combination each time a pulse from the oscillator isimpressed upon said one stage whereby, after a predetermined number ofpulses from said oscillator, said counter produces an output pulse, andsaid electronic control means including means operative responsively t0the counter output pulse to terminate operation of the oscillator.

11. An apparatus for producing a variable number of voltage pulses in agroup, comprising an oscillator for generating voltage pulses,electronic control means connected to the oscillator to initiate andterminate operation thereof, said electronic control means includingmeans operative responsively to a control signal to initiate operationof the oscillator in exact phase relation therewith, permuting countermeans having a plurality of stages including a first stage coupled tothe oscillator and a last stage, means conditioning said stages toefiect interaction of certain of said stages in a predeterminedcombination when a pulse from the oscillator is im pressed upon saidfirst stage, and automatically to change the combination at eachsuccessive pulse applied to the first stage until the last stageproduces an output pulse after a predetermined number of pulses areapplied to the first stage, and said electronic control means includingmeans operative responsively to the output pulse of the last stage toterminate operation of the oscillator.

12. An apparatus for producing a group of periodic pulses in precisetime relation with a controlling influence, comprising periodic pulsegenerating means, electronic control means perative responsively to thecontrolling influence to initiate operation of said generating means inexact phase relation therewith, counting means fed by the generatingmeans to produce an ou put pulse when a predetermined number of pulsesare counted thereby, and electronic con trol means operativeresponsively to the output 01 the counting means to terminate operationof the generating means.

13. The method of producing a predetermined number of periodicelectrical energy pulses in precise time relation with a control signalwhich comprises precisionally initiating generation of equally-spacedelectrical energy pulses responsively to the control signal with thefirst electrical energy pulse abruptly generated in exact phase relationwith the control signal, counting each of the generated electricalenergy pulses, and abruptly terminating generation of the electricalenergy pulses when a number of pulses equal to said predetermined numberare counted.

14. The method of operating an electrical energy pulse oscillationgenerator to produce a 10 I predetermined number of electrical energypulses in precise time relation with a controlling influence, whichcomprises precisionally initiating operation of the oscillationgenerator responsivelyjto the controlling influence to produce periodicelectrical energy pulses with the first'electrical gy pulse abruptlygenerated in exact phase relation with the controlling influence,counting each of the electrical energy pulses produced by the pulseoscillation generator, producing a control signal when a predeterminednumber of electrical energy pulses are counted, and abruptly terminatingoperation oi. the oscillation generator responsively to the controlsignal.

CLAUD E. CLEET'ON.

REFERENCES CITED i'flhe following references are of record in the fileof this patent:

UNITED STATES PATENTSh Number Name Date 11,923,345 Wallace Aug."22,1933' l-, 934,322* Osbon Nov. 7, 1933 $027,038 Hansell Jan. 7', 193623136532 Knoll et a1. Apr. 7, 1936 2,106,831 Dawson Feb. 1, 1938 2,132,654 Smith Oct. 11, 1938 2,272,070 Reeves Feb. 3, 1942- FORE'IGNPATENTS Number Country Date 355,705 Great Britain Aug. 24, 1941 OTHERREFERENCES Uffelmann: "A Thyratron Counterf, Journal of ScientificInstruments, vol. 15 (1238). pp. 222-226. Lifeshutz and Lawson: "A'Iriodev Vacuum Tube Scale-of-Two Circuit, Review of ScientificInstruments, vol. 9, March 1938, pages.83-89.

